Without limiting the scope of the invention, its background is described in connection with a portable computer system coupled to an expansion base unit housing one or more peripheral devices which are operably linked to the portable computer.
Standard bus architectures have been routinely employed as interfaces connecting the core microcomputer system to peripheral devices such as floppy disk drives, CD drives, printers, sound boards, tape backup systems, pointing devices and others for some time now. Popular examples of such bus architectures include the the Industry Standard Architecture (ISA), the Extended Industry Standard Architecture (EISA), the Micro Channel and NuBus. The introduction of advanced and higher speed computer systems, however, has created a need for an efficient high speed interface to communicate with peripheral devices. The response to this need was the development and adoption of the Peripheral Component Interface (PCI) standard.
A PCI bus is a synchronous, processor-independent 32-bit or 64-bit local bus that offers several key advantages over bus structures such a ISA and EISA. Compared to older architectures, PCI permits higher bus speeds (up to 33 Mhz), increased data transfer rates and independence from a particular processor or local bus arrangement.
Furthermore, PCI requires less printed circuit board (PCB) area compared to other bus implementations due to its relatively small pin count (49 pins for a Master PCI and 47 pins for a PCI target). Thus, it is common for computer manufacturers to offer one or more PCI slots on their desktop computers along side one or more ISA, EISA slots or other standard interface.
The use of the PCI architecture has been, until recently, primarily restricted to desktop computer systems. PCI use on portable systems such as laptops and notebook computers has been hindered for several reasons. First, portable systems have smaller PCB real estate limiting the size and quantity of circuitry. Second, since most portables operate on rechargeable batteries, any additional circuitry would drain available power, increase the frequency of battery recharge or replacement and divert power from other subsystems within the unit.
A popular addition to the portable computer system is commonly referred to as the expansion base or "docking" unit. In essence, a portable computer system is coupled to an expansion base via one or more physical connector(s) or via a single host bridge. The expansion base, in turn, houses one or more peripheral device such as a hard disk, sound card, video card and the like, which are driven by the portable computer's microprocessor.